use rustc::middle::const_eval;
use rustc::middle::ty::{self, TyCtxt};
use rustc::mir::mir_map::MirMap;
use rustc::mir::repr as mir;
use std::error::Error;
use std::fmt;

use memory::{FieldRepr, IntRepr, Memory, Pointer, Repr};

const TRACE_EXECUTION: bool = true;

#[derive(Clone, Debug)]
pub enum EvalError {
    DanglingPointerDeref,
    InvalidBool,
    PointerOutOfBounds,
}

pub type EvalResult<T> = Result<T, EvalError>;

impl Error for EvalError {
    fn description(&self) -> &str {
        match *self {
            EvalError::DanglingPointerDeref => "dangling pointer was dereferenced",
            EvalError::InvalidBool => "invalid boolean value read",
            EvalError::PointerOutOfBounds => "pointer offset outside bounds of allocation",
        }
    }

    fn cause(&self) -> Option<&Error> { None }
}

impl fmt::Display for EvalError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.description())
    }
}

/// A stack frame.
struct Frame<'a, 'tcx: 'a> {
    /// The MIR for the fucntion called on this frame.
    mir: &'a mir::Mir<'tcx>,

    /// A pointer for writing the return value of the current call, if it's not a diverging call.
    return_ptr: Option<Pointer>,

    /// The list of locals for the current function, stored in order as
    /// `[arguments..., variables..., temporaries...]`. The variables begin at `self.var_offset`
    /// and the temporaries at `self.temp_offset`.
    locals: Vec<Pointer>,

    /// The offset of the first variable in `self.locals`.
    var_offset: usize,

    /// The offset of the first temporary in `self.locals`.
    temp_offset: usize,
}

impl<'a, 'tcx: 'a> Frame<'a, 'tcx> {
    fn arg_ptr(&self, i: u32) -> Pointer {
        self.locals[i as usize]
    }

    fn var_ptr(&self, i: u32) -> Pointer {
        self.locals[self.var_offset + i as usize]
    }

    fn temp_ptr(&self, i: u32) -> Pointer {
        self.locals[self.temp_offset + i as usize]
    }
}

struct Interpreter<'a, 'tcx: 'a> {
    tcx: &'a TyCtxt<'tcx>,
    mir_map: &'a MirMap<'tcx>,
    memory: Memory,
    stack: Vec<Frame<'a, 'tcx>>,
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub enum PrimVal {
    Bool(bool),
    I8(i8),
    I16(i16),
    I32(i32),
    I64(i64),
}

impl<'a, 'tcx: 'a> Interpreter<'a, 'tcx> {
    fn new(tcx: &'a TyCtxt<'tcx>, mir_map: &'a MirMap<'tcx>) -> Self {
        Interpreter {
            tcx: tcx,
            mir_map: mir_map,
            memory: Memory::new(),
            stack: Vec::new(),
        }
    }

    fn push_stack_frame(&mut self, mir: &'a mir::Mir<'tcx>, args: &[&mir::Operand<'tcx>],
                        return_ptr: Option<Pointer>) -> EvalResult<()> {
        let num_args = mir.arg_decls.len();
        let num_vars = mir.var_decls.len();
        let num_temps = mir.temp_decls.len();
        assert_eq!(args.len(), num_args);

        let mut locals = Vec::with_capacity(num_args + num_vars + num_temps);

        for (arg_decl, arg_operand) in mir.arg_decls.iter().zip(args) {
            let repr = self.ty_to_repr(arg_decl.ty);
            let dest = self.memory.allocate(repr.size());
            let (src, _) = try!(self.eval_operand(arg_operand));
            try!(self.memory.copy(src, dest, repr.size()));
            locals.push(dest);
        }

        let var_tys = mir.var_decls.iter().map(|v| v.ty);
        let temp_tys = mir.temp_decls.iter().map(|t| t.ty);
        locals.extend(var_tys.chain(temp_tys).map(|ty| {
            let repr = self.ty_to_repr(ty).size();
            self.memory.allocate(repr)
        }));

        self.stack.push(Frame {
            mir: mir,
            return_ptr: return_ptr,
            locals: locals,
            var_offset: num_args,
            temp_offset: num_args + num_vars,
        });

        Ok(())
    }

    fn pop_stack_frame(&mut self) {
        let _frame = self.stack.pop().expect("tried to pop a stack frame, but there were none");
        // TODO(tsion): Deallocate local variables.
    }

    fn call(&mut self, mir: &'a mir::Mir<'tcx>, args: &[&mir::Operand<'tcx>],
            return_ptr: Option<Pointer>) -> EvalResult<()> {
        try!(self.push_stack_frame(mir, args, return_ptr));
        let mut current_block = mir::START_BLOCK;

        loop {
            if TRACE_EXECUTION { println!("Entering block: {:?}", current_block); }
            let block_data = mir.basic_block_data(current_block);

            for stmt in &block_data.statements {
                if TRACE_EXECUTION { println!("{:?}", stmt); }
                let mir::StatementKind::Assign(ref lvalue, ref rvalue) = stmt.kind;
                try!(self.eval_assignment(lvalue, rvalue));
            }

            if TRACE_EXECUTION { println!("{:?}", block_data.terminator()); }

            use rustc::mir::repr::Terminator::*;
            match *block_data.terminator() {
                Return => break,

                Goto { target } => current_block = target,

                If { ref cond, targets: (then_target, else_target) } => {
                    let (cond_ptr, _) = try!(self.eval_operand(cond));
                    let cond_val = try!(self.memory.read_bool(cond_ptr));
                    current_block = if cond_val { then_target } else { else_target };
                }

                SwitchInt { ref discr, ref values, ref targets, .. } => {
                    // FIXME(tsion): Handle non-integer switch types.
                    let (discr_ptr, discr_repr) = try!(self.eval_lvalue(discr));
                    let discr_val = try!(self.memory.read_i64(discr_ptr));

                    // Branch to the `otherwise` case by default, if no match is found.
                    current_block = targets[targets.len() - 1];

                    for (index, val_const) in values.iter().enumerate() {
                        let ptr = try!(self.const_to_ptr(val_const));
                        let val = try!(self.memory.read_i64(ptr));
                        if discr_val == val {
                            current_block = targets[index];
                            break;
                        }
                    }
                }

                // Call { ref func, ref args, ref destination, .. } => {
                //     use rustc::middle::cstore::CrateStore;
                //     let ptr = destination.as_ref().map(|&(ref lv, _)| self.lvalue_to_ptr(lv));
                //     let func_val = self.operand_to_ptr(func);

                //     if let Value::Func(def_id) = func_val {
                //         let mir_data;
                //         let mir = match self.tcx.map.as_local_node_id(def_id) {
                //             Some(node_id) => self.mir_map.map.get(&node_id).unwrap(),
                //             None => {
                //                 let cstore = &self.tcx.sess.cstore;
                //                 mir_data = cstore.maybe_get_item_mir(self.tcx, def_id).unwrap();
                //                 &mir_data
                //             }
                //         };

                //         let arg_vals: Vec<Value> =
                //             args.iter().map(|arg| self.operand_to_ptr(arg)).collect();

                //         self.call(mir, &arg_vals, ptr);

                //         if let Some((_, target)) = *destination {
                //             current_block = target;
                //         }
                //     } else {
                //         panic!("tried to call a non-function value: {:?}", func_val);
                //     }
                // }

                // Switch { ref discr, ref targets, .. } => {
                //     let discr_val = self.read_lvalue(discr);

                //     if let Value::Adt { variant, .. } = discr_val {
                //         current_block = targets[variant];
                //     } else {
                //         panic!("Switch on non-Adt value: {:?}", discr_val);
                //     }
                // }

                Drop { target, .. } => {
                    // TODO: Handle destructors and dynamic drop.
                    current_block = target;
                }

                Resume => unimplemented!(),
                _ => unimplemented!(),
            }
        }

        self.pop_stack_frame();
        Ok(())
    }

    fn eval_binary_op(&mut self, bin_op: mir::BinOp, left_operand: &mir::Operand<'tcx>,
                      right_operand: &mir::Operand<'tcx>, dest: Pointer) -> EvalResult<()>
    {
        // FIXME(tsion): Check for non-integer binary operations.
        let (left, left_repr) = try!(self.eval_operand(left_operand));
        let (right, right_repr) = try!(self.eval_operand(right_operand));

        let left_val = try!(self.memory.read_primval(left, &left_repr));
        let right_val = try!(self.memory.read_primval(right, &right_repr));

        use rustc::mir::repr::BinOp::*;
        use self::PrimVal::*;
        let result_val = match (bin_op, left_val, right_val) {
            (Add,    I64(l), I64(r)) => I64(l + r),
            (Sub,    I64(l), I64(r)) => I64(l - r),
            (Mul,    I64(l), I64(r)) => I64(l * r),
            (Div,    I64(l), I64(r)) => I64(l / r),
            (Rem,    I64(l), I64(r)) => I64(l % r),
            (BitXor, I64(l), I64(r)) => I64(l ^ r),
            (BitAnd, I64(l), I64(r)) => I64(l & r),
            (BitOr,  I64(l), I64(r)) => I64(l | r),
            (Shl,    I64(l), I64(r)) => I64(l << r),
            (Shr,    I64(l), I64(r)) => I64(l >> r),
            (Eq,     I64(l), I64(r)) => Bool(l == r),
            (Lt,     I64(l), I64(r)) => Bool(l < r),
            (Le,     I64(l), I64(r)) => Bool(l <= r),
            (Ne,     I64(l), I64(r)) => Bool(l != r),
            (Ge,     I64(l), I64(r)) => Bool(l >= r),
            (Gt,     I64(l), I64(r)) => Bool(l > r),
            _ => unimplemented!(),
        };

        self.memory.write_primval(dest, result_val)
    }

    fn assign_to_product(&mut self, dest: Pointer, dest_repr: &Repr,
                         operands: &[mir::Operand<'tcx>]) -> EvalResult<()> {
        match *dest_repr {
            Repr::Product { ref fields, .. } => {
                for (field, operand) in fields.iter().zip(operands) {
                    let (src, _) = try!(self.eval_operand(operand));
                    try!(self.memory.copy(src, dest.offset(field.offset), field.repr.size()));
                }
            }
            _ => panic!("expected Repr::Product target"),
        }
        Ok(())
    }

    fn eval_assignment(&mut self, lvalue: &mir::Lvalue<'tcx>, rvalue: &mir::Rvalue<'tcx>)
        -> EvalResult<()>
    {
        let (dest, dest_repr) = try!(self.eval_lvalue(lvalue));

        use rustc::mir::repr::Rvalue::*;
        match *rvalue {
            Use(ref operand) => {
                let (src, _) = try!(self.eval_operand(operand));
                self.memory.copy(src, dest, dest_repr.size())
            }

            BinaryOp(bin_op, ref left, ref right) =>
                self.eval_binary_op(bin_op, left, right, dest),

            UnaryOp(un_op, ref operand) => {
                let (src, src_repr) = try!(self.eval_operand(operand));
                let src_val = try!(self.memory.read_primval(src, &src_repr));

                use rustc::mir::repr::UnOp::*;
                use self::PrimVal::*;
                let result_val = match (un_op, src_val) {
                    (Not, Bool(b)) => Bool(!b),
                    (Not, I64(n)) => I64(!n),
                    (Neg, I64(n)) => I64(-n),
                    _ => unimplemented!(),
                };

                self.memory.write_primval(dest, result_val)
            }

            Aggregate(ref kind, ref operands) => {
                use rustc::mir::repr::AggregateKind::*;
                match *kind {
                    Tuple => self.assign_to_product(dest, &dest_repr, operands),

                    Adt(ref adt_def, variant_idx, _) => match adt_def.adt_kind() {
                        ty::AdtKind::Struct => self.assign_to_product(dest, &dest_repr, operands),

                        ty::AdtKind::Enum => match dest_repr {
                            Repr::Sum { discr_size, ref variants, .. } => {
                                // TODO(tsion): Write the discriminant value.
                                self.assign_to_product(
                                    dest.offset(discr_size),
                                    &variants[variant_idx],
                                    operands
                                )
                            }
                            _ => panic!("expected Repr::Sum target"),
                        }
                    },

                    Vec => unimplemented!(),
                    Closure(..) => unimplemented!(),
                }
            }

            // Ref(_region, _kind, ref lvalue) => {
            //     Value::Pointer(self.lvalue_to_ptr(lvalue))
            // }

            ref r => panic!("can't handle rvalue: {:?}", r),
        }
    }

    fn eval_operand(&mut self, op: &mir::Operand<'tcx>) -> EvalResult<(Pointer, Repr)> {
        use rustc::mir::repr::Operand::*;
        match *op {
            Consume(ref lvalue) => self.eval_lvalue(lvalue),

            Constant(mir::Constant { ref literal, ty, .. }) => {
                use rustc::mir::repr::Literal::*;
                match *literal {
                    Value { ref value } => Ok((
                        try!(self.const_to_ptr(value)),
                        self.ty_to_repr(ty),
                    )),
                    ref l => panic!("can't handle item literal: {:?}", l),
                }
            }
        }
    }

    fn eval_lvalue(&self, lvalue: &mir::Lvalue<'tcx>) -> EvalResult<(Pointer, Repr)> {
        let frame = self.current_frame();

        use rustc::mir::repr::Lvalue::*;
        let ptr = match *lvalue {
            ReturnPointer =>
                frame.return_ptr.expect("ReturnPointer used in a function with no return value"),
            Arg(i) => frame.arg_ptr(i),
            Var(i) => frame.var_ptr(i),
            Temp(i) => frame.temp_ptr(i),
            ref l => panic!("can't handle lvalue: {:?}", l),
        };

        let ty = self.current_frame().mir.lvalue_ty(self.tcx, lvalue).to_ty(self.tcx);
        Ok((ptr, self.ty_to_repr(ty)))

        //     mir::Lvalue::Projection(ref proj) => {
        //         let base_ptr = self.lvalue_to_ptr(&proj.base);

        //         match proj.elem {
        //             mir::ProjectionElem::Field(field, _) => {
        //                 base_ptr.offset(field.index())
        //             }

        //             mir::ProjectionElem::Downcast(_, variant) => {
        //                 let adt_val = self.read_pointer(base_ptr);
        //                 if let Value::Adt { variant: actual_variant, data_ptr } = adt_val {
        //                     debug_assert_eq!(variant, actual_variant);
        //                     data_ptr
        //                 } else {
        //                     panic!("Downcast attempted on non-ADT: {:?}", adt_val)
        //                 }
        //             }

        //             mir::ProjectionElem::Deref => {
        //                 let ptr_val = self.read_pointer(base_ptr);
        //                 if let Value::Pointer(ptr) = ptr_val {
        //                     ptr
        //                 } else {
        //                     panic!("Deref attempted on non-pointer: {:?}", ptr_val)
        //                 }
        //             }

        //             mir::ProjectionElem::Index(ref _operand) => unimplemented!(),
        //             mir::ProjectionElem::ConstantIndex { .. } => unimplemented!(),
        //         }
        //     }

        //     _ => unimplemented!(),
        // }
    }

    fn const_to_ptr(&mut self, const_val: &const_eval::ConstVal) -> EvalResult<Pointer> {
        use rustc::middle::const_eval::ConstVal::*;
        match *const_val {
            Float(_f) => unimplemented!(),
            Int(n) => {
                // TODO(tsion): Check int constant type.
                let ptr = self.memory.allocate(8);
                try!(self.memory.write_i64(ptr, n));
                Ok(ptr)
            }
            Uint(_u)          => unimplemented!(),
            Str(ref _s)       => unimplemented!(),
            ByteStr(ref _bs)  => unimplemented!(),
            Bool(b) => {
                let ptr = self.memory.allocate(Repr::Bool.size());
                try!(self.memory.write_bool(ptr, b));
                Ok(ptr)
            },
            Struct(_node_id)  => unimplemented!(),
            Tuple(_node_id)   => unimplemented!(),
            Function(_def_id) => unimplemented!(),
            Array(_, _)       => unimplemented!(),
            Repeat(_, _)      => unimplemented!(),
        }
    }

    fn make_product_repr<I>(&self, iter: I) -> Repr where I: IntoIterator<Item = ty::Ty<'tcx>> {
        let mut size = 0;
        let fields = iter.into_iter().map(|ty| {
            let repr = self.ty_to_repr(ty);
            let old_size = size;
            size += repr.size();
            FieldRepr { offset: old_size, repr: repr }
        }).collect();
        Repr::Product { size: size, fields: fields }
    }

    // TODO(tsion): Cache these outputs.
    fn ty_to_repr(&self, ty: ty::Ty<'tcx>) -> Repr {
        use syntax::ast::IntTy;
        match ty.sty {
            ty::TyBool => Repr::Bool,

            ty::TyInt(IntTy::Is) => unimplemented!(),
            ty::TyInt(IntTy::I8) => Repr::Int(IntRepr::I8),
            ty::TyInt(IntTy::I16) => Repr::Int(IntRepr::I16),
            ty::TyInt(IntTy::I32) => Repr::Int(IntRepr::I32),
            ty::TyInt(IntTy::I64) => Repr::Int(IntRepr::I64),

            ty::TyTuple(ref fields) => self.make_product_repr(fields.iter().cloned()),

            ty::TyEnum(adt_def, ref subst) => {
                let num_variants = adt_def.variants.len();

                let discr_size = if num_variants <= 1 {
                    0
                } else if num_variants <= 1 << 8 {
                    1
                } else if num_variants <= 1 << 16 {
                    2
                } else if num_variants <= 1 << 32 {
                    4
                } else {
                    8
                };

                let variants: Vec<Repr> = adt_def.variants.iter().map(|v| {
                    let field_tys = v.fields.iter().map(|f| f.ty(self.tcx, subst));
                    self.make_product_repr(field_tys)
                }).collect();

                Repr::Sum {
                    discr_size: discr_size,
                    max_variant_size: variants.iter().map(Repr::size).max().unwrap_or(0),
                    variants: variants,
                }
            }

            ty::TyStruct(adt_def, ref subst) => {
                assert_eq!(adt_def.variants.len(), 1);
                let field_tys = adt_def.variants[0].fields.iter().map(|f| f.ty(self.tcx, subst));
                self.make_product_repr(field_tys)
            }

            ref t => panic!("can't convert type to repr: {:?}", t),
        }
    }


    fn current_frame(&self) -> &Frame<'a, 'tcx> {
        self.stack.last().expect("no call frames exist")
    }
}

pub fn interpret_start_points<'tcx>(tcx: &TyCtxt<'tcx>, mir_map: &MirMap<'tcx>) {
    for (&id, mir) in &mir_map.map {
        for attr in tcx.map.attrs(id) {
            use syntax::attr::AttrMetaMethods;
            if attr.check_name("miri_run") {
                let item = tcx.map.expect_item(id);

                println!("Interpreting: {}", item.name);

                let mut miri = Interpreter::new(tcx, mir_map);
                let return_ptr = match mir.return_ty {
                    ty::FnConverging(ty) => {
                        let repr = miri.ty_to_repr(ty).size();
                        Some(miri.memory.allocate(repr))
                    }
                    ty::FnDiverging => None,
                };
                miri.call(mir, &[], return_ptr).unwrap();

                if let Some(ret) = return_ptr {
                    println!("Returned: {:?}\n", miri.memory.get(ret.alloc_id).unwrap());
                }
            }
        }
    }
}